Agricultural production increased significantly
during the first and second five-year development plans (Repelita
I and 11) in Indonesia. This increase was due more to
improvements in the technology of plantgrowing (i.e., the
application of mineral fertilizers, the introduction of
high-yielding varieties, the adoption of strict plant protection,
and the introduction of new planting techniques) than to
improvements in post-harvest technology (i.e., handling, storage,
and processing of the harvest). As a consequence of this lopsided
attention, a significant portion of the harvest has not been
efficiently utilized. Because these under-used residues contain
considerable amounts of carbohydrates, proteins, lipids,
vitamins, and minerals, it is imperative that ways be found to
use them. Otherwise they will be wasted and their potential
benefits lost.

This paper presents a brief overview on the
present status of agricultural residues, their utilization, the
prospect for intensifying and expanding their uses as raw
materials for bioconversion, and the constraints to be overcome
in order to achieve that objective.

In this paper, the following definitions are
used:

residues, the end-products of
production that have not been salvaged or recycled. Their
economic value is less than the cost of collection and
transformation for use.

bioconversion, conversion of
organic materials with the help of micro-organisms.

Rice (Oriza saliva) is the staple food
of Indonesia. It is widely cultivated in the country on wet as
well as on dry lands, particularly on the six major islands and
island groups: Java-Madura, Sumatra, Sulawesi, Bali-Nusa
Tenggara, Kalimantan, and Maluku-lrian Jaya, in that order of
importance. Its cultivation and processing are labour-intensive
and require a large capital input. Therefore, it is not
surprising that more than 60 per cent of the total paddy produced
in 1976 (approximately 30 million tons) originated from
Java-Madura, the most densely populated as well as the most
developed and fertile islands in Indonesia.

Because of the magnitude of the harvest and the
fact that the method of harvesting and post-harvest processing is
largely manual, paddy production generates a huge amount of
residues. These consist of straw or stalks, husks or hulls, and
bran. The total amount of straw generated in 1976 was about 37.5
million tons; of husks, approximately 6.8 million tons; and of
bran, about 3 million tons.

The bulk of the straw is left rotting in the
field, sometimes after burning, or is ploughed back into the soil
as a conditioner and organic fertilizer. A large proportion of
the straw is also used as cattle bedding and feed. As a feed it
contains approximately 66 per cent dry matter, 3.4 per cent crude
protein, 0.73 per cent digestible protein, and 38.1 per cent
total digestible nutrients. A significant quantity of the straw
also serves as raw material for board and paper manufacturing.
Straw is an excellent substrate for the cultivation of paddy
straw mushrooms (Volvariella volvacea). This is widely
practiced in West Central Java as a home industry. Under
favourable conditions, a yield of 6 per cent is quite usual.

Some of the rice husks are used for fuel. Some
of the ash generated is used as washing powder, but the bulk is
wasted. Most of the husks around large rice mills, however, are
also wasted. In some areas, significant quantities of husks serve
as a component of cattle feed. The husk has a quality comparable
to that of straw because it contains 91 per cent dry matter, with
3.8 per cent crude protein,1.2 per cent digestible protein, and
19.55 per cent total digestible nutrients.

Although a significant amount of the bran is
used as a component of cattle and chicken feed, a larger
proportion is not used as it should be. As feed, it contains
about 90 per cent dry matter, 10.3 per cent crude protein, and
6.78 per cent digestible protein.

Maize

Maize (Zea mays) is the second staple
for many Indonesians, particularly those in Madura, Nusa
Tenggara, and Sulawesi. It is mainly cultivated on dry lands in a
multiple cropping system. Compared to rice, its cultivation and
processing demand less labour and capital input. Major producing
islands are in the following order of importance: Java-Madura,
Sulawesi, Bali-Nusa Tenggara, Sumatra, Maluku-lrian Jaya, and
Kalimantan. Total production in 1976 amounted to more than 2.5
million tons, the bulk of which (about 71 per cent) came from
Java-Madura.

Most harvesting and post-harvest processing of
maize are still manual operations that generate a large amount of
residues, including stalks, husks, skins, cobs, pressed cake, and
bran. It is estimated that stalk production per hectare is
between two and four tons. Thus, the total quantity of stalks
generated in 1976 was between 4 and 8 million tons. The husks,
skins, and cobs produced as the result of separating the grains
amounted to 1.7,0.34, and 2 million tons,.

Most of the stalks, husks, and skins are left
to rot or ploughed back into the soil as a conditioner and an
organic fertilizer. A significant proportion of the stalks -
particularly the fresh, young ones - are used as green fodder.
Stalks have relatively good feed nutritive values, containing
about 21 per cent dry matter,1.7 per cent crude protein,1.1 per
cent digestible protein, and 16.3 per cent total digestible
nutrients. Dried stalks are often used as fuel.

Some of the husks and skin trimmings are also
fed to cattle. In fact, they have better feed nutritive values
than those of fresh stalks, because they contain higher
digestible protein (18.1 vs.1.1 per cent) and higher total
digestible nutrients (67.2 vs.16.3 per cent).

A by-product of the oil extraction process is
presscake. With its content of 18.1 per cent digestible protein
and 74.1 per cent total digestible nutrients, it has a feed
nutritive value comparable to that of the whole grain.

Cassava

Cassava (Manihot utilissima) is an
important food crop, particularly in places where the soil is
relatively poor or in times of food scarcity. It is also an
important export commodity in the form of pellets and chips. The
plant is widely cultivated in the country either as a monoculture
or in a multiple-cropping system. It does not need special
attention or large capital input. Major producing islands are in
the following order of importance: Java-Madura, Bali-Nusa
Tenggara, Sumatra, Sulawesi, Kalimantan, and Maluku-lrian Jaya.
Total production in 1976 was around 12 million tons, 73 per cent
of which came from Java-Madura.

Since only the roots are collected, harvesting
cassava yields large quantities of residue in the form of woody
stems, leaves, and soft plant parts. If a mature cassava plant
consists of 50 per cent roofs, 30 per cent woody stems, and 20
per cent soft plant parts and leaves, the total residues
generated at harvest time in 1976 alone amounted to 7.2 million
tons of woody stems and 4.8 million tons of soft parts and
leaves.

The roots are usually further processed into
pellets, chips, or tapioca flour. The processing generates
residues as peels and tapioca flour wastes. The total quantity of
peels produced in 1976 was approximately 2.4 million tons. Since
only about 10 per cent of total cassava production is processed
into flour, the flour wastes generated in 1976 were approximately
0.27 million tons.

Most of the woody stems are generally burned as
fuel, while the soft plant parts and leaves - particularly those
of non-toxic varieties - are fed to cattle or left on the soil as
a conditioner and fertilizer. A significant amount is also used
as green fodder, which has good feed values, containing 26 per
cent dry matter, 23.1 per cent crude protein, and 13.86 per cent
digestible crude protein.

Significant proportions of the peels are fed to
cattle, and contain about 5.3 per cent crude protein, 20.9 per
cent crude fibre, 1.6 per cent ether extracts, 65.7 per cent
nitrogen-free extract, and 6.1 per cent ash. Most of the peels,
however, are not used.

The bulk of the flour waste is used as a
component of feedstuff. It contains about 90.3 per cent dry
matter, 5.6 per cent crude protein, and 3.73 per cent digestible
protein. A small amount is also used as a component for the
preparation of traditional fermented foods such as oncom
(fermented peanut presscake) and tempeh.

Soybeans

Soybeans (Glycine max) are one of the
important crops of Indonesia, serving as the raw material of many
soybean-based traditional fermented and non-fermented foods, such
as tempeh, kecap, taoco, and tahu. It is usually planted in
monoculture in rotation with rice. In places with low rainfall,
multiple cropping of soybeans with other crops is commonly
practiced. Compared to rice, soybean cultivation requires less
attention and capital input. Total production in 1976 was about
500,000 tons. The largest share came from Java-Madura, followed
successively by Bali-Nusa Tenggara, Sumatra, Sulawesi,
Kalimantan, and Maluku - Irian Jaya.

Harvesting and separating the seeds from the
pods generate residues in the form of straw and shells. Total
straw production in 1976 was about 550,000 tons, while that of
shells was approximately 50,000 tons. Significant amounts of
residues are produced as the result of processing soybeans into
foods. In tempeh preparation, for example, about 28 per cent of
the raw material is wasted. Approximately the same proportion
(27.4 per cent) is wasted in tabu (soy curd) production. If, in
1973 alone, tempeh and tahu production amounted to 18,000 tons,
then the total residues generated amounted to approximately 5,000
tons. No information is available regarding the proportion of
residues generated in kecap preparation, but, considering that in
1973 more than 5.5 million litres of kecap were produced, there
is no question that the amount of residues is considerable.

The dry straw and shells are usually burned as
fuel or left on the field and ploughed back into the soil as a
conditioner and fertilizer. The young plant parts and leaves,
however, are fed to cattle as green fodder. They have good
nutritive value, containing 27.9 per cent dry matter, 24.7 per
cent crude protein, and 12.53 per cent digestible crude protein.

No information is available on the use of the
bulk of tempeh residues, but in some parts of Java a small
proportion of solid residue is used as one of the raw materials
for the preparation of second-class tempeh and kecap In the case
of tahu residues, the solid portion is usually fed to pigs as a
feed component. It contains 22.84 per cent protein, 7.27 per cent
fat, 65.42 per cent carbon, and 4.47 per cent ash. The liquid
portion is usually discharged into the sewers, causing a
considerable pollution problem.

Groundnuts

Groundnuts (Arachis hypogaea) are the
second important crop among the pulses in Indonesia. They are
widely used as an ingredient of many Indonesian foods and also as
a source of vegetable oil. As in the case of soybeans, they are
usually planted in monoculture in rotation with rice, while in
places with low rainfall they are part of a multiple-crop system.
Their cultivation requires about the same amount of labour and
capital input needed for soybean production. Total production in
1976 amounted to 300,000 tons, the largest proportion of which
(74.54 per cent) came from Java-Madura. Other producing islands
are in the following order of importance: Sumatra, Sulawesi,
Bali-Nusa Tenggara, Kalimantan, and Maluku-lrian Jaya.

The residues from groundnut production are
mainly generated at harvest and during separation of the seeds
from the pods, i.e., stems and shells. In 1976 alone a total of
about 330,000 tons of stems and 9,900 tons of shells resulted
from harvesting and processing. Moreover, oil-extraction
processing of the seeds also generates residues in the form of
presscake. If about 50 per cent of the total production is used
for oil production, then the cake generated in 1976 amounted to
about 120,000 tons.

The stems and leaves are mostly fed to cattle
as green fodder or as plant meal. In both forms they have
relatively good nutritive values. Green fodder contains 17.6 per
cent dry matter, 19.9 per cent crude protein, and 13.08 per cent
digestible crude protein, whereas plant meal contains 88 per cent
dry matter and 16.6 per cent crude protein. Stems that are not
suitable for feed are usually left on the field and ploughed into
the soil as a conditioner and fertilizer. The dry shells are
commonly burned as fuel.

The bulk of the presscake is utilized as an
ingredient of feed. It contains 90.15 per cent dry matter, 44.9
per cent crude protein, and 41.32 per cent digestible protein. A
significant amount of high-quality presscake constitutes the main
ingredient in oncom (fermented groundnut presscake) preparation.

Coconuts

Indonesia is the second largest producer of
coconuts (Cocos nucifera) in the world after the
Philippines, and copra is one of the more important export
commodities. Coconuts grow extensively in the country, covering
an area of not less than 2 million hectares. Major producing
islands are Sulawesi, Maluku-lrian Jaya, and Bali-Nusa Tenggara.
Total production in 1976 was about 3,483 million nuts, or the
equivalent of about 6.6 million tons of unhusked nuts and 1.4
million tons of copra.

Coconut is a general-purpose fruit, as
practically all parts of it are usable. Husks, coir dust, and
shells are the residues after the shelled nut has been obtained.
In the preparation of copra from shelled nuts, additional residue
is generated in the form of liquid Finally, as the result of oil
extraction from copra, coconut presscake is obtained. The amounts
of the respective residues in 1976 were approximately as follows:
husks, 2.2 million tons, consisting of 1.5 million tons of coir
dust and 0.7 million tons of fibre and outer rind; shells, 0.4
million tons; liquid, 0.7 million tons; presscake, 0.4 million
tons.

Most of the husks are wasted, but a significant
quantity are used for mats and matting, floor coverings, brushes,
strong ropes, etc. The shells usually serve as fuel for drying
copra. In recent years there has been some interest in using
shells to produce activated charcoal. Practically all of the
liquid is wasted, and in many cope-producing centres it causes a
serious pollution problem. In some places in Java the presscake
is consumed as a side dish, but the majority serves as a feed
ingredient. It has relatively good feed nutritive values,
containing 91 per cent dry matter, 21.3 per cent crude protein,
and 18.2 per cent digestible crude protein.

Oil Palm

Oil palm (Elaeis guineensis) is an
important export commodity for Indonesia. It is mostly planted on
large plantations in Sumatra. In 1976 alone it covered 179,000
hectares, with a total production of about 433,000 tons of oil.

Harvesting the fruit and the oil-extracting
process generate considerable amounts of residues as empty
stalks, fibres, pulp (pericarps), shells, and cake. The amounts
of the respective residues generated in 1976 were approximately:
empty stalks, 0.6 million tons; fibre, 0.2 million tons; pulp,
0.8 million tons; shells, 0.3 million tons; cake, 0.6 million
tons. Most of the empty stalks, pulp, fibre, and shells are
burned as fuel in the factory. The cake generally serves as an
ingredient in cattle feed.

Sugar Cane

Although Indonesia is no longer an exporter of
cane sugar, sugar cane (Saccharum officinarum) still is
an important crop in the country. It is mostly planted on large
plantations in Java. In recent years, however, new plantations
have been started in Sumatra and Sulawesi, while sugar cane
planting by small-holders has also been expanding. In 1976 the
planted area covered about 0.2 million hectares. Total refined
sugar production in the same year was about 1.3 million tons,
with 1 million tons produced by the estates and 0.3 million tons
by small-holders.

Cane sugar production generates a large amount
of residues, both at the time of harvesting and during the
sugar-extracting process. At harvest the main residues are cane
tops, while those associated with sugar extraction are molasses,
bagasse, and pith. Residues in 1976 amounted to about 3.4 million
tons of cane tops, 0.6 million tons of molasses, 3.3 million tons
of bagasse, and 1.1 million tons of pith.

Fresh cane tops are commonly used as green
fodder. They contain 2.7 per cent digestible protein and 45.7 per
cent total digestible nutrients. The dry tops and leaves,
however, are left on the soil and (sometimes after burning)
ploughed back into it as a conditioner and fertilizer. Large
amounts of the bagasse and pith are used as fuels in the factory.
They are also important as raw materials for the production of
board and paper, but the amount used is not large.

Most of the molasses is exported. Only a small
proportion of it is fermented into alcohol domestically, and a
still smaller proportion serves as a component of cattle feed.
Molasses has a relatively good feed value, containing 74.7 per
cent dry matter, 6.5 per cent crude protein, and 3.7 per cent
digestible protein.

Rubber

Indonesia is one of the major rubber producers
in the world. The plant (Hevea brasiliensis) is widely
cultivated in Sumatra, Kalimantan, and Java, on big plantations
as well as in small-holdings. In 1976 the area planted was about
2.3 million hectares, producing aporoximately 0.8 million tons of
dry rubber.

Latex contains about 4 per cent non-rubber
constituents, most of which are in the serum fraction. During
latex processing, the serum fraction is washed away. These
non-rubber components are protein (1 per cent w/w), lipids (1 per
cent w/w), carbohydrates - mostly quebrachitol (1 per cent w/w),
inorganic salts - largely phosphates, K, Mg, Na, Ca, Fe, and Cu
(0.5 per cent w/w), among others. Except for the lipids, most of
the carbohydrates, inorganic salts, and 67 per cent of the latex
proteins are in the serum. Thus, approximately 3.5 per cent of
the latex is washed away during rubber processing. Assuming dry
rubber production in 1976 was about 0.8 million tons (the
equivalent of about 2.5 million tons of latex), the non-rubber
constituents wasted would have amounted to 17,000 tons of
proteins, 25,000 tons of carbohydrates, and 12,000 tons of
inorganic salts. They are usually discharged into open streams,
thus causing a serious pollution problem.

Coffee

Coffee (Coffea robusta) is one of the
most important export commodities of Indonesia. Throughout Asia,
only India's coffee production exceeds that of Indonesia. It is
cultivated particularly in the highlands of Java and Sumatra. In
1976 the planted area was about 0.4 million hectares, producing
about 185,000 tons of dry beans.

Coffee processing generates residues in the
form of pulp or husk, hull, and bean. These represent
approximately 78, 6, and 16 per cent of the berry. Thus, the
residues generated in 1976 amounted to about 309,000 tons of
fresh pulp and 24,000 tons of fresh hulls.

No information is available on the use of these
residues, but it has been reported that the pulp has a relatively
good feed value, containing 91.8 per cent dry matter, 9.2 per
cent protein, 3.4 per cent digestible crude protein, and 42.2 per
cent total digestible nutrients.

Forestry Products

The importance of forestry products as export
commodities is exceeded only by petroleum. In 1977, wood exports
totalled more than 15.8 million tons, with a value of US$951.2
million. Tropical forest covers much of Indonesia. In 1976 it
covered more than 122 million hectares, producing approximately
16.3 million m³ of wood. This consisted of 14.6 million m³ of
logs and 1.7 million m³ of boards. More than 65 per cent of the
total came from Kalimantan, about 22.9 per cent from Sumatra, and
the remaining 12.1 per cent from the other islands.

Logging and wood processing generate a
considerable number of residues in the form of logging wastes,
defective logs, sawdust, edgings, slabs, and trimmings. In 1976,
logging trees with a diameter larger than 30 cm generated more
than 3.1 million m³ logging wastes and 1.7 million m³ defective
logs. Processing the logs in saw mills generated more than 0.37
million m³ sawdust, 0.9 million m³ edgings and slabs, and 0.61
million m³ trimmings. Practically all of the logging debris is
left in the forests. This is also the case with the bulk of
wood-processing residues, except for an insignificant amount that
is burned as fuel.

Livestock

The important domesticated animals in Indonesia
include cattle, buffaloes, horses, goats, sheep, pigs, and
poultry (chickens and ducks). The total livestock population in
1976 was about 108 million. More than 58 per cent of the animals
were in Java-Madura, 21 per cent were in Sumatra, and the
remaining 21 per cent were on the other islands.

No information is available on the residues of
slaughterhouses in Indonesia, but there are data on the manure
produced by these animals. The total annual production of fresh
manure is approximately as follows (in kilograms per head):
cattle, 5,400; horses, 2,700; pigs, 1,500; sheep and goats, 500;
and poultry, 13.

Except for human wastes, most manures are used
as organic fertilizers. Only recently has there been an increased
interest in using manure as a raw material for biogas production.
This practice is still very limited, however.

Traditional fermented foods such as tempeh,
oncom, tape, kecap, and taoco are widely consumed in
Indonesia. With the exception of oncom and tape, most of these
products are based on whole soybeans. Tape is fermented cassava
or glutinous rice, whereas oncom is a fermented peanut/groundnut
presscake or solid residue of tahu.

Besides improving the nutritive value,
attractiveness, and taste of the raw material, microbial
fermentation, in some cases, also extends the shelf-life and
reduces the toxic substances present in the basic ingredients.

Owing to the high price of the raw materials
commonly used in traditional food fermentation and the abundance
of agricultural residues in Indonesia, it would apparently be
more economical to utilize certain residues as substitutes for
some of the raw materials. These residues may be used singly
(e.g., solid waste of tabu for black oncom preparation), or in
combination (e.g., a combination of peanut presscake, solid waste
of tahu, and solid waste of tapioca flour for red oncom
preparation). A number of residues that deserve to be studied
further as raw materials for traditional fermented foods are:
peanut presscake, coconut presscake, cononut liquid, and the
solid residues of tahu, tapioca flour, and tempeh.

As most traditional fermented foods are
manufactured on a small scale as home industries using relatively
simple techniques and non-sterile conditions, the quality of the
end-product often varies from batch to batch or from time to
time. Thus, appropriate microbial cultures as well as reliable
and appropriate techniques should be developed if a product with
a uniform quality is desired.

Animal Feed

As outlined in the preceding section, fresh
residues from a number of crops (e.g., maize, cassava, soybeans,
groundnuts, and sugar cane) have relatively good feed values.

Because of their seasonal availability there
are times of surplus or deficit in supplies of these residues. It
is desirable, of course, to have enough available year-round.
This probably can be realized by conserving excess fresh residues
at harvest time as silage. By this means, not only could residues
be kept much longer but their feed value would also be improved.
Silage of fresh maize stalks and leaves, for instance, contains
higher levels of crude protein (1.9 vs. 1.7 per cent) and total
digestible nutrients (18.3 vs. 16.3 per cent) than the fresh
material, while its digestible protein content remains the same.

Making silage from agricultural residues has
not been extensively practiced in Indonesia. However, considering
the abundance and varieties of residues, as well as the fact that
most of the livestock is raised on Java and Madura, the time has
come to pay more attention to this important aspect of animal
husbandry.

Of the many residues, the following deserve
particular attention: rice straw, fresh maize stems and leaves,
young cassava stems and fresh leaves, fresh soybean stems and
leaves, fresh groundnut stems and leaves, sugar cane tops, and
fresh coffee pulp. Because these residues are widely dispersed,
the silage-making technique should be simple and appropriate for
implementation by small farmers.

The presscakes resulting from oil extraction of
groundnuts, coconuts, and oil palm seeds also deserve further
study as animal feed supplements.

Mushroom Cultivation on Agricultural Residues

Volvariella volvacea is probably the
most suitable type of mushroom for cultivation in Indonesia. It
has been grown here for a long time, largely on paddy straw, and
a yield of 6 per cent is not unusual. Studies that have been
conducted in many Asian countries show that V. volvacea
grows well on:

paddy straw, giving a yield of 4.6 per
cent,

oil palm pericarp waste, with a 4.7 per
cent yield,

cotton waste, with a 28.7 per cent yield,

sugar cane waste, with a 12.4 per cent
yield.

In order to maximize the use of available
agricultural residues, the most appropriate technique and
substrate for a particular environment should be selected. Of the
many residues, attention should be given especially to paddy
straw, oil palm pericarp, dry maize stems and leaves, sugar cane
bagasse, dry soybean shells, dry peanut shells, coconut husks,
and sawdust.

Biogas Practically any agricultural residues
can be utilized as raw materials for biogas production under
suitable conditions provided that the C/N ratio is correct. Most
of the principles and technical aspects of biogas production are
known. In fact, a number of prototypes of biogas generators were
developed in Indonesia and are operating in some places on Java.
The main factors hampering the wider use of biogas at present are
economic rather than technical.

Organic Fertilizer

As discussed earlier, the bulk of many
agricultural residues is left on the field or ploughed back into
the soil as a conditioner and fertilizer. In certain soils, the
incorporation of fresh residues, particularly those with a high
C/N ratio, may result in severe nitrogen immobilization.
Therefore, it would be much safer if residues such as rice straw,
dry maize stems, sugar cane bagasse, and others with a high C/N
ratio were composted first, before being incorporated into the
soil as fertilizer.

Most of the principles and technical aspects
for composting agricultural residues are known. However, some
technical problems in conducting efficient small-scale composting
under tropical conditions remain to be solved, such as the
minimum size of the pile, the rate of aerating it, the size of
the particles, the amount of watering, the effect of residue
composition, simple criteria for determining the maturity of the
compost, etc.

Owing to the scattered distribution and
seasonal availability of the residues, small-scale composting
will probably be more economical than a large-scale operation.
For example, a number of composting plants have been built in
Medan and Surabaya, but there seem to be many obstacles to
operating them economically.

Single-Cell Protein (SCP)

Although it probably will not be economical to
carry out large-scale SCP production under present conditions in
Indonesia, the abundance of raw materials such as molasses,
rubber serum, coconut liquid, and liquid waste from cassava flour
extraction could justify the initiation of research on a
laboratory scale. Some problems that deserve to be studied are
the selection of active thermo-tolerant strains of
microorganisms, optimal conditions for fermenting the different
residues, the appropriate scale of production, the technique for
separating the end-product, etc.

Should SCP production eventually be realized in
Indonesia, the plants should preferably be located near the
source of the raw material. Thus, if molasses is used as the
substrate, the plant should be located near or at a sugar
refinery. The production scale should also be adjusted to
existing facilities, and the micro-organisms should be
thermo-tolerant in order to minimize energy consumption for
cooling the fermentors. In this way, production costs could be
kept as low as possible.

Constraints vary with the residues, but, for
the most part, they include the lack of economic incentives,
assured markets, capital, and managerial initiative. The
technology is usually available, but because of the seasonal
availability and dispersed distribution of most of the residues,
some adjustments will be required to process smaller quantities
of residues under tropical conditions. Thus, there is a need for
conducting research to adapt technologies for the most
appropriate small-scale processing of residues.

Agricultural crop residues are abundant both in
kind and quantity. Currently, most of them are wasted on the
fields or ploughed back into the soil as conditioners and organic
fertilizers. Because of their relatively good feed values, some
are also used as animal feed. A much smaller quantity, through
bioconversion, serves as raw material for some traditional
fermented foods, as well as substrates for mushroom cultivation.
However, considerable amounts of copra and rubber-processing
residues, e.g., coconut liquid and rubber serum, are still
discharged into the environment, causing a serious pollution
problem. Because of the lack of economic incentives, capital,
managerial initiatives, and, in some cases, suitable technology,
progress in wider use of residues is much slower than it would be
if there were no such constraints.

Bhushan, B. Agricultural Residues and Their
Utilization in Some Countries of South and South East Asia.
Residues Utilization - Management of Agricultural and
Agro-industrial Wastes, industry Sector Seminars. FAO, Rome,
1977.